Ferrule with internal recess and cylindrical wall

ABSTRACT

High localized loading, galling, and high torque forces have been generally eliminated or greatly reduced in a two ferrule tube fitting assembly through suitable modification of the rear ferrule so as to redirect the reaction forces acting between the front ferrule and the drive nut. The rear ferrule has a cylindrical interior wall that closely surrounds the tube end and is provided on the interior cylindrical wall with a circumferentially continuous radial recess that is located between the nose and rear wall of the rear ferrule. The rear ferrule also has a radially external wall that is substantially conical and additionally shaped to extend radially outward toward the enlarged diameter portion or flange of the rear ferrule.

BACKGROUND OF THE INVENTION

The subject invention is directed to the art of ferrule type tubefittings. More particularly, the invention concerns a two ferrulefitting wherein the rear ferrule is designed to reduce the torquerequired to rotate the associated nut and to also reduce galling betweenthe rear ferrule and the interior surface of the drive nut.

A commercially available and highly successful two ferrule fitting usedfor tubing is illustrated in FIGS. 1 and 1A. FIG. 1 shows the fittingcomponents in a finger tight position preparatory to final tightening,whereas FIG. 1A shows the fitting after final tightening. As shown, thefitting comprises a body 10 having a cylindrical opening 12 counterboredfor receiving tube end 13. A tapered, frusto-conical camming mouth 14 islocated at the axial outer end of the counterbore. A front ferrule 16having a smooth, cylindrical inner wall 18 is closely received on thetube. The front ferrule has a frusto-conical outer surface 20 to bereceived in the camming mouth.

Associated with the front ferrule 16 and located axially outwardtherefrom is a rear ferrule 22 configured as shown with a tapered noseportion 24 and a rear flange 26 having an inclined end surface 28. Thetapered nose enters a tapered camming surface in the rear surface of thefront ferrule.

The ferrules 16, 22 are enclosed by a drive nut member 30 threaded tothe body. During tightening and make-up of the fitting, the inner endface, flange, or shoulder 32 of the nut acts against the rear wall ofthe rear ferrule to drive the ferrules forwardly into the fully engagedposition shown in FIG. 1A.

The small diameter portion or nose of the rear ferrule is dimensioned sothat it plastically deforms during make-up of the fitting. This actionis desirable since it results in tight gripping engagement of the outerwall of the tubing. The thickness of the nose portion cannot be reducedto an extent that the rear ferrule deforms too much and only the rearferrule adequately grips the outer wall of the tubing. That is, the twoferrule assembly requires desired deformation of both the front and rearferrules for the gripping and sealing capabilities that have made thistwo ferrule assembly a commercially successful product. On the otherhand, the thickness of the nose of the rear ferrule cannot be enlargedto such an extent that it results in a structural arrangement that istoo stiff and does not permit the desired rear ferrule deformation.

Accordingly, it will be recognized by those skilled in the art that apredetermined wall thickness of the nose of the rear ferrule is desiredthat achieves the desired gripping of the tube and cooperates with thefront ferrule in such a manner that it achieves its desired goals ofgripping and sealing the tube.

It is also recognized that operators of fluid systems test the systemprior to a production run by pressurizing the system to an appropriatefactor times the rated system pressure. In this manner, the operator caneasily detect whether the fluid system is sealed, i.e. that there are noleaks. With this knowledge, the manufacturer can provide a fitting inwhich the nose of the rear ferrule will not have any additional plasticdeformation at the elevated test pressure. Accordingly, the elevatedtest pressure is used to determine the desired wall thickness of thenose portion of the rear ferrule to achieve the desired amount ofdeformation of the nose and permit the front and rear ferrules toproperly grip and seal with the outer wall of the tube.

It has also been found that galling of the drive nut sometimes occurs inthe drive face area of engagement between the inner end face of the nutand the rear wall of the rear ferrule. After analysis, it is believedthat the axial thrust between the front and rear ferrule is essentiallyparallel to the axis of the fitting. This axial thrust causes the rearcorner region of the rear ferrule to selectively concentrate at theinside drive surface of the nut in a localized area to produce thegalling. This also noticeably increases the nut torque forcesexperienced during make-up even if galling is absent. Accordingly, itwould be highly desirable to provide a design wherein the thrust forcesdo not produce the high localized loading with the resultant galling andhigh torque forces.

SUMMARY OF THE INVENTION

In accordance with the subject invention, the high localized loading,galling, and high torque forces have been generally eliminated orgreatly reduced through suitable modification of the rear ferrule so asto redirect the reaction forces acting between the front ferrule and thedrive nut.

In particular, and in accordance with the subject invention, the rearferrule has a cylindrical interior wall that closely surrounds the tubeend and is provided on the interior cylindrical wall with acircumferentially continuous radial recess that is located between thenose and rear wall of the rear ferrule.

In accordance with another aspect of the invention, a tube fitting ofthe general type is provided wherein the rear ferrule has a radiallyexternal wall that is substantially conical and additionally shaped toextend radially outward toward the enlarged diameter portion or flangeof the rear ferrule.

Both the radial recess and the conical wall feature of the nose portionin the rear ferrule cause those reaction forces generated during fittingmake-up and passing from the front ferrule through the rear ferrule tothe nut to take on a more uniform distribution across the inner face ofthe nut to thereby reduce any concentration of force acting axiallyagainst the inner face of the nut member.

It has been found that the conical shape of the radially external walland the recess provided on the cylindrical interior wall of the ferrulecan have a variety of different configurations. The actual shape andconfiguration of this circumferentially continuous recess can bedetermined through experimentation or analysis in line with theparameters and general objectives outlined in the Background.Preferably, however, the recess has a length that is at least about fivepercent (5%) of the total overall axial length of the rear ferrule. Inaddition, it has been found desirable to provide the ferrule with aradial extent that is at least about five percent (5%) of the radialextent of the rear wall of the rear ferrule.

By careful design of the radially external wall and the recess relativeto the remainder of the rear ferrule, the reaction forces are shifted soas to have a greater radial component. This achieves a more uniformdistribution and prevents highly localized loading anywhere at the rearface of the rear ferrule and the inner wall of the nut member actingagainst the rear ferrule. Because the reaction forces are redirected inthis manner, there is, of course, less concentration and a reduction inboth galling and torque requirements during fitting make-up.

As can be seen from the foregoing, the primary object of the inventionis the provision of a two ferrule fitting wherein galling between thenut and the force receiving surface of the rear ferrule is greatlyreduced.

Yet another object of the invention is the provision of a two ferrulefitting assembly which uses a modified rear ferrule that results inlower torque requirements on fitting make-up.

Yet another object is the provision of a fitting of the general typedescribed wherein the ferrules and the nut member are arranged toproduce a more desirable force distribution with improved cooperationbetween the nut and the rear ferrule.

Still other advantages and benefits of the invention will becomeapparent to those skilled in the art upon a reading and understanding ofthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, preferred embodiments and a method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 is a longitudinal cross-sectional view of a well known prior arttwo ferrule swage-type fitting;

FIG. 1A is an enlarged view of the circled area of FIG. 1 showing theprior art fitting in a made-up condition;

FIG. 2 is a view like FIG. 1 but showing a preferred embodiment of afitting incorporating a modified rear ferrule designed to improvereaction force transmission through the rear ferrule;

FIG. 3 is a greatly enlarged showing of the circled area of FIG. 2;

FIG. 4 is a detailed, partial cross-sectional view of a preferred formof rear ferrule;

FIG. 5 is a cross-sectional view similar to FIG. 4 showing a secondpreferred form for the rear ferrule;

FIG. 6 is a cross-sectional view of the fitting of FIG. 1 particularlyshowing the rear ferrule positioned between the front ferrule and thenut at initial make-up;

FIG. 7 is a view of the fitting of FIG. 6 in a made-up condition andillustrating the force concentrations;

FIG. 8 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention;

FIG. 9 is a view of the fitting of FIG. 8 in a made-up condition andillustrating the force concentrations;

FIG. 10 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention;

FIG. 11 is a view of the fitting of FIG. 10 in a made-up condition andillustrating the force concentrations;

FIG. 12 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention;

FIG. 13 is a view of the fitting of FIG. 12 in a made-up condition andillustrating the force concentrations; and

FIG. 14 is a table of different geometrical variations of the rearferrule configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposesof illustrating preferred embodiments of the invention only and not forpurposes of limiting same, FIGS. 2-4 illustrate the overall arrangementof a fitting incorporating the invention. The FIGS. 2-4 embodiment hasthe major components identified with the same reference numerals usedwith respect to the description of the prior art device of FIGS. 1 and1A. A description of a FIG. 1 element is to be taken as equallyapplicable to the FIGS. 2-4 elements that are correspondingly numberedunless otherwise noted. In particular, in the FIGS. 2-4 embodiment, therear ferrule 22′ has been modified in a manner to cause the reactionforces acting between the front ferrule through the rear ferrule to thenut to have a significant force component that is directed radiallyoutward. This is in contradistinction to the FIGS. 1 and 1A embodimentwherein the force component under consideration has a high axialcomponent. Specifically, as shown in FIG. 4, force component A extendsgenerally axially of the rear ferrule 22′ and results in an increase inthe loads applied at the radial inner face of the ferrule surface 28′and the flange 32′ of the nut. As previously discussed, high localizedloading or force concentration in this area produces high torque andgalling.

In the preferred form of the invention, a redirection of the reactionforces is achieved by providing a circumferential recess 40 throughoutthe inner surface of the ferrule 22′. Note that a recess 40 is locatedgenerally midway between the opposite ends of the ferrule 22′ and thisresults in the inner surface of the rear ferrule being reduced to tworelatively narrow contact areas 42 and 44. By so modifying the rearferrule, the forces which are conducted from the front ferrule throughthe rear ferrule to the nut surface or flange 32′ tend to be directedmore radially outward such as diagrammatically illustrated by the forceline B of FIG. 4.

Another important feature of the invention is best exemplified bycomparing the rear ferrule of FIG. 1 with the rear ferrule of the FIGS.2-4 embodiment. Particularly, the outer radial wall 50 of the rearferrule includes a conical section that increases in radial dimension asit extends from the forward nose portion, that is received in the rearchamfer region 52 of the front ferrule, to the rear flange 26′. In theprior art arrangement (FIGS. 1 and 1A), the rear ferrule has acylindrical throughbore and an outer radial wall that extends parallelto the inner surface defining the throughbore in this region. In otherwords, the rear ferrule has a constant annular wall thickness “t”. Inthe embodiment of FIGS. 2-4, the outer wall has the conical or taperedconfiguration that provides sufficient wall thickness “t” and controlleddeformation of the nose portion when the recess is incorporated into themodified rear ferrule. Preferably, the outer wall 50 has a generallyuniform angle or taper as it extends between the reduced dimension noseregion 52 received in the camming mouth of the front ferrule and theenlarged diameter rear flange 26′. Again, this provides controlleddeformation of the rear ferrule so that the region 52 is plasticallydeformed radially inward along surface 44 into gripping, sealedengagement with the outer wall of the tube.

FIG. 5 illustrates another preferred embodiment of the rear ferrule inwhich the recess 40 has is defined by two different angles (an obtusetriangle). For example, the smaller first angle defined with the innersurface increases as it extends rearwardly from the surface 44 towardthe rear flange 26′. The larger second angle (approximately twice theangular dimension of the first angle) increases as it extends forwardlyfrom the surface 42 toward the nose region. These angles thus intersectat an axial position that is located beneath the intersection of theouter wall 50 with the rear flange. Accordingly, the forces are moreevenly distributed over the rear face 28′.

Turning to FIGS. 6 and 7, the rear ferrule of the prior art arrangementof FIG. 1 is shown before and after make-up of the fitting. The fittingwas subjected to a finite element analysis, the results of which areparticularly evident in FIG. 7. There, shaded regions in the rear flangeof the rear ferrule and the nut evidence the force and stressconcentrations encountered upon make-up of the fitting. Particularly, aregion of high stress concentration is designated at area 60. Regions ofprogressively decreased stress concentration are identified by numerals62, 64, 66, 68, and 70. Thus, the large stress concentration at theradial inner location of the rear face 28′ results in increased torqueduring make-up and potential galling of the nut.

FIGS. 8 and 9 show another modified rear ferrule in accordance with theteachings of the present invention. This rear ferrule is the same asshown in FIG. 5. As particularly evident in FIG. 9, the region of highstress concentration is substantially reduced in size when compared toFIG. 7. This indicates that the forces have been more uniformlydispersed over the rear face of the flange of the rear ferrule. Thus,the torque is reduced and the potential for galling is likewise reduced.

FIGS. 10 and 11 represent the rear ferrule shown and described in FIG.4. Here, the finite element analysis illustrates that the region of highstress concentration is substantially removed at the rear face and amore uniform distribution of forces obtained. Again, the torque forcesassociated with make-up are thus reduced with the correspondingreduction in localized force concentrations. The recess and conicalouter wall provide a radial component to the forces generated in thefitting and transferred through the rear ferrule while still providing adesired gripping and sealing of the tube.

The embodiment of FIGS. 12 and 13 also achieves these same objectives.The recess is of a slightly different configuration, i.e., the recess ismore sharply defined in the inner wall of the rear ferrule. It is alsoshifted slightly forwardly so that the deepest portion of the recess islocated forwardly of the rear flange. However, the outer wall is stillof conical configuration and in conjunction with the recess distributesthe forces along the rear face of the rear ferrule.

As is apparent with the various embodiments described above, the recessand the tapered outer wall do not require a particular conformation toachieve the force distribution and reduced torque for make-up of thefitting. In fact, a number of proposed alternative embodiments areillustrated in table form in FIG. 14. For example, the first row ofgeometries have a standard location that is generally defined as therear edge of the recess being located axially beneath the intersectionof the outer wall and the enlarged flange. The tear drop, righttriangle, rectangle, oval, square circular, obtuse triangle, curve, andcompound curve are various shapes that the recess may adopt. Moreover,the recess can be positioned at a forward location (second row), or arearward location where the deepest portion of the recess is positionedbeneath the enlarged flange (third row) while still adopting the variousconfigurations. Still further, the orientation of the shapes can bereversed as demonstrated by the various geometries in the fourth row orthe sixth row, or the recess may be defined by multiple recesses asshown in the geometries of the fifth and eighth rows. Alternatively, therecess(es) may be enlarged as indicated in the seventh and eighth rows.Accordingly, the invention is not limited to the particularconfigurations shown and described in the earlier embodiments of FIGS.2-13, but may also be incorporated into selected other geometricalconfigurations.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

Having thus described the invention, it is claimed:
 1. In a tube fittingof the type including a fitting body having a cylindrical bore closelyreceiving a tube end, a tapered counterbore surrounding the tube end anddefining the entrance to the bore, a nut member threaded to the fittingbody and cooperating with the fitting body to define a chamber enclosingthe tube end, a front ferrule surrounding the tube end with a taperednose extending into the tapered counterbore and a rear wall locatedaxially outward, a rear ferrule having a rear wall engaged by an axialinner end wall of the nut member and a tapered nose extending into atapered recess formed in the rear wall of the front ferrule, theimprovement wherein the rear ferrule has a cylindrical interior wallthat closely surrounds the tube end with the cylindrical interior wallhaving a circumferentially continuous radial recess located between therear ferrule's nose and rear wall to cause reaction forces generatedduring fitting make-up and passing from the front ferrule through therear ferrule to the nut to have a significant force component that isdirected radially outward to thereby reduce the force component actingaxially against the radial inner portion of the inner end wall of thenut member.
 2. The improvement as defined in claim 1 wherein the radialrecess increases in radial depth as one progresses axially from adjacentthe nose of the rear ferrule toward the rear wall of the rear ferrule.3. The improvement as defined in claim 1 wherein the rear wall of therear ferrule is slightly inclined toward the nose of the rear ferrule.4. The improvement as defined in claim 1 wherein the rear ferruleincludes a radially extending flange that defines the rear wall of therear ferrule.
 5. The improvement as defined in claim 4 wherein theradially extending flange has a forward face located rearwardly of thenose portion of the rear ferrule and spaced from the rear wall of thefront ferrule when the nose of the rear ferrule is fully inserted intothe tapered recess formed in the rear wall of the front ferrule.
 6. Theimprovement as defined in claim 1 wherein the rear ferrule has atapering outer wall between the nose portion and the rear wall fordirecting forces radially outward.
 7. The improvement as defined inclaim 1 wherein said circumferentially continuous radial recess has anaxial length of approximately five percent minimum of the total axiallength of the rear ferrule.
 8. The improvement as defined in claim 1wherein said circumferentially continuous radial recess in said rearferrule includes first and second axially spaced recesses.
 9. Theimprovement as defined in claim 1 wherein the rear ferrule includes aradially extending flange that defines the rear wall of the rearferrule, the recess being located at substantially the same axialposition as the flange.
 10. The improvement as defined in claim 1wherein the rear ferrule includes a radially extending flange thatdefines the rear wall of the rear ferrule, and a tapering outer wallbetween the nose portion and the flange for directing forces radiallyoutward.
 11. The improvement as defined in claim 10 wherein the taperingouter wall increases in the radial direction as it extends from the noseportion toward the flange.
 12. In a tube fitting of the type including afitting body having a cylindrical bore closely receiving a tube end, atapered counterbore surrounding the tube end and defining the entranceto the bore, a nut member threaded to the fitting body and cooperatingwith the fitting body to define a chamber enclosing the tube end, afront ferrule surrounding the tube end with a tapered nose extendinginto the tapered counterbore and a rear wall located axially outward, arear ferrule having a rear wall engaged by an axial inner end wall ofthe nut member and a tapered nose extending into a tapered recess formedin the rear wall of the front ferrule, the improvement wherein the rearferrule has a cylindrical interior wall that closely surrounds the tubeend with the cylindrical interior wall having a circumferentiallycontinuous radial recess located between the rear ferrule's nose andrear wall, and a tapering outer wall portion disposed between the rearwall and the nose of the rear ferrule to cause reaction forces generatedduring fitting make-up and passing from the front ferrule through therear ferrule to the nut to have a significant force component that isdirected radially outward to thereby reduce the force component actingaxially against the radial inner portion of the inner end wall of thenut member.
 13. The improvement as defined in claim 12 wherein therecess is disposed at substantially the same axial location as theflange.
 14. The improvement as defined in claim 12 wherein the recess isdefined by first and second axially spaced recesses.
 15. The improvementas defined in claim 12 wherein the recess is located radially inward ofthe tapering outer wall.